Inferring spatial patterns of mercury exposure in migratory boreal songbirds: Combining feather mercury and stable isotope (δ2H) measurements

Migratory songbirds breeding in the Canadian Boreal forest are exposed to mercury (Hg), a potent neurotoxin that impairs avian health, however, the degree of exposure depends on many factors. As breeding grounds are geographically remote and vast, themeasurement of Hg in individual birds is impractical particularly at large spatial scales. Here, we present a Canada-wide dataset of nearly 2000 migratory songbirds that were used to assess summer Hg exposure of 15 songbird species sampled during fall migration. We measured Hg concentrations in tail feathers and related those to dietary guild, geographic capture location, age, sex and probable breeding ground locations using feather delta H-2. Overall mean (+/- SE) feather Hg concentration was 1.49 +/- 0.03 mu g/g (N = 1946): however, a clear geographic gradient in feather Hg concentrations emerged being highest in East and lowest inWest. Dietary guild was the next strongest predictor of feather Hg with insectivorous songbirds in Eastern Canada at particular risk due to Hg exposure on summer breeding grounds. This broad-scale assessment of Hg exposure in migratory songbirds in Canada can be used to guide future studies on finer-scale determinants of Hg exposure in birds. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

Migratory songbirds breeding in the Canadian Boreal forest are exposed to mercury, with exposure levels depending on various factors. A Canada-wide dataset of nearly 2000 migratory songbirds showed a clear geographic gradient in feather mercury concentrations and dietary guild as a strong predictor of feather mercury levels.